Environmental zyxwvutsrqponmlkjih Toxicology and Chemislry, zyxwvutsrqponml VoI. zyxwvutsrqponm 1 I, pp. 1427-1439, 1992 Printed zyxwvutsrqponml In the USA. Pergamon Press Ltd. 0730-7268/92 zyxwv $5.00 + .OO Copyright zyxwv 0 zyx 1992 SETAC RESPONSE OF HEPATIC MFO ACTIVITY AND PLASMA SEX STEROIDS TO SECONDARY TREATMENT OF BLEACHED KRAFT PULP MILL EFFLUENT AND MILL SHUTDOWN K.R. MUNKITTRICK,*t G.J. VAN DER KRAAK,~ M.E. MCMASTER,~ and C.B. PORTT 11 ?Great Lakes Laboratory for Fisheries and Aquatic Sciences, Department of Fisheries and Oceans, 867 Lakeshore Road, Burlington, Ontario, L7R 4A6 Canada $Department of Zoology, University of Guelph, Guelph, Ontario, NlG 2W1 Canada §Department of Biology, University of Waterloo, Ontario, N2L 3G1 Canada IIC. Portt & Associates, 56 Waterloo Avenue, Guelph, Ontario, NIH 3H5 Canada (Received 28 June 1991; Accepted 5 January 1992) Abstract -The discharge of bleached kraft mill effluent (BKME) into Jackfish Bay, Lake Superior, Canada, has been associated with a number of changes in the physiology and whole organism re- sponses of four fish species. Current studies have been following physiological indicators of BKME impact for evidence of improvement after the installation of a secondary treatment system. Second- ary treatment has not been successful in eliminating BKME impacts on hepatic mixed-function ox- ygenase (MFO) activity in white sucker (Catostomus commersonr] because fish collected from Jackfish Bay after initiation of secondary treatment exhibited similar MFO activity as recorded in samples collected during two previous years. Hepatic MFO activity was also induced in long-nose sucker (Catostomus catostomus), lake whitefish (Coregonus clupeaformis), and lake trout (Salve- linus namaycush) after secondary treatment. However, samples collected two weeks after a planned mill maintenance shutdown showed no MFO induction in long-nose sucker, reduced MFO activity in white sucker, and a reduced impact zone for MFO induction in lake whitefish. A reduction in circulating levels of gonadal sex steroids has also been recorded in fish exposed to primary-treated BKME in Jackfish Bay. In contrast, neither secondary treatment nor mill shutdown was success- ful in eliminating impacts of BKME exposure on levels of testosterone and 170-estradiol in female white sucker and long-nose sucker. The short duration of MFO induction after shutdown and the persistence of steroid reductions suggest that (a) secondary treatment has not been successful in re- moving “MFO-active” compounds from BKME, (b) induction is not related to sediment contami- nation with persistent compounds, (c) the inducing agents are rapidly cleared by fish, and (d) effects on steroids may not be directly related to MFO induction. Keywords- Bleached kraft pulp mill effluent MFO activity EROD Testosterone 17P-Estradiol INTRODUCTION Hepatic mixed-function oxygenase (MFO) en- zyme activity has been proposed as an indicator for delineating zones of exposure to inducing agents [1,2]. Induced MFO activities have been found in fish downstream of bleached kraft mills in Ontario [3-51, other Canadian provinces [6,7], and Scandi- navia [8-lo]. The chemicals responsible for the en- zyme induction near bleached kraft pulp mills have not been identified, although polychlorinated di- *To whom correspondence may be addressed. The current address of M.E. McMaster is Great Lakes Laboratory for Fisheries and Aquatic Sciences, 867 Lakeshore Rd., Burlington, Ontario, L7R 4A6 Canada. benzofurans and dibenzo-p-dioxins have been sug- gested as causative agents [6,7]. Over the past three years, we have been study- ing the impacts of bleached kraft mill effluent (BKME) on Jackfish Bay, Lake Superior, Canada, which has received BKME input since 1949. The study site is isolated and is the receiver of no other industrial or domestic effluents. Studies conducted in 1988 [4] and 1989 [11,12] examined fish re- sponses when the BKME received only primary treatment to remove fiber and suspended solids be- fore its release. Identified impacts of primary- treated BKME were induced MFO activity and an altered suite of responses related to reproduction: 1427